An oil or gas well relies on the inflow of hydrocarbon petroleum products. Horizontal well completions are a routine economic exploitation technique in certain formations for increased hydrocarbon inflow. The ability to steer while drilling allows operators to drill theses wells from the surface, instead of sending mining crews downhole. When drilling an oil or gas well, an operator may decide to leave productive intervals uncased (open hole) to expose porosity and permit unrestricted wellbore inflow of hydrocarbon petroleum products. Non-cemented horizontal well completions includes true open hole completions, slotted or perforated-liner completions, or liner completions with external casing packers. Cased and cemented completions can also be used on horizontal wells, which are perforated to permit inflow through the openings created. Reservoir rock properties and the owner/operator's initial investment influence the appropriate completion selection. Generally, most horizontal wells in competent formations receive open hole completions.
Often, wells drilled and completed in low-permeability formations sustain formation damage, thereby limiting productivity. For increased productivity and improved economics, these wells must be stimulated with pumping stimulation fluids, such as fracturing fluids, acid, cleaning chemicals and/or proppant laden fluids to improve wellbore inflow.
The hydraulic fracturing technique creates a fracture extending from a borehole into rock formation in an effort to increase or restore the rate in which fluids can be produced from the formation surrounding the borehole. When applied to the stimulation of oil and gas wells, the objective of hydraulic fracturing is to increase the amount of exposure a well has to the surrounding formation and to provide a conductive channel through which the fluid can flow easily to the well.
In hydraulic fracturing, pressurized fluid fractures the formation. Fluid pressure in the wellbore is increased until it exceeds the formations breakdown pressure, creating one or more fractures at the wellbore. This pressure is commonly known as the fracture initiation pressure. After the well is fractured, the pressure necessary for the fracture to grow, the fracture extension pressure, is generally less than the fracture initiation pressure.
In formations with sufficient vertical permeability, fracturing is unnecessary. Because they are economical, uncased horizontal completions have become commonplace. However, if these wells need to be stimulated, excessive flow rates are often required to fracture these wells because the extremely large wall surface of the wellbore allows fluid to leak off into the formation. Furthermore, when a fracture initiates, stored energy (pressure) will force fluid into the fracture causing unwanted propagation. This problem might also be encountered as a result of excessively high pumping rates, where control of the pressure development might be less accurate.
An industry solution includes static diversion techniques that typically use mechanical systems to divert fluid flow into a short section of the formation. One such device, known as the straddle-packer systems, uses two hydraulically activated packers located a few feet apart. Fracturing fluids are injected into the well section between the two packers. However, the system has proven ineffective due to near-wellbore stress distribution causing fractures to jump past the packers and communicate to other sectors of the wellbore. Furthermore, static diversion techniques have proven ineffective, impractical, and uneconomical. Additionally, in long horizontal wells (as long as 6000 ft) straddle packers are not typically utilized.
Hydrajet fracturing is another commonly utilized industry technique. The hydrajet fracturing technique, based on a Bernoulli equation, maintains low wellbore pressure and initiates strategically placed fractures. While pumping fracturing fluids through the jets, the operator uses flow down the annulus to control bottom hole pressure and to supplement the proper fracture with fluid. Because the well becomes supercharged during fracturing, operators must use tools to maintain annulus pressure during pipe movement and install a tubing value in the tubing string downhole to allow new connections to be made in the tubing. Each fracture can be formulated with different fluids such as sand slurries or acid, depending on the rock formation surrounding the fracture entry point. Moreover, numerous small fractures can be placed through the well, bypassing damaged areas.
While the described methods assist in producing fractures, it is problematic and difficult to selectively choose the desired location and propagation of the fracture in horizontal open hole wells due to long horizontal wells (as long as 6000 ft) with varying stresses and lithology along the wellbore. Thus, the goal of the present invention is to provide a method for selective placement, initiation and propagation of a hydraulically induced fracture.